There is known a wireless power transmitting apparatus including a power transmitting device and a power receiving device receiving power from the power transmitting device. The wireless power transmitting apparatus has a problem in that load variation or the like generates excessive inrush current, resulting in breaking of an active device such as a transistor on a power receiving side. Conventionally, in order to address this problem, a method of preventing inrush current by shorting a circuit on the power receiving side to separate a resonator circuit has been adopted.
The conventional method is effective for protecting elements on the power receiving side. However, there is a possibility that gradual increase in power transmission voltage in a state where a load impedance is high (light load) generates excessive current in a device on a power transmitting side. This results in breaking of elements on the power transmitting side. Furthermore, it is required to use a device tolerant to a higher current value than that in an actual power transmitting state, as a power transmitting device. This leads to increase in cost of the device.